1. Field of the Invention
The present invention relates to a video disk playback apparatus for playing back a disk on which high definition video signals are recorded and, in particular, relates to a video disk playback device for playing back a disk on which video signals other than high definition video signals are recorded.
2. Description of the Prior Art
As one of several new television broadcasting methods, high definition television (hereinafter referred to as HDTV) has been proposed. As an output of a HDTV television camera, each primary color signal of R, G, and B occupies a band width of 30 MHz. A signal in this band width is compressed. Thereby, a component signal which is composed of for example a luminance signal with a band width of 22 MHz and two color difference signals with a band width 6 MHz is formed. When the component signal is recorded on an optical type video disk, with respect to the luminance signal, the time base expansion process is performed. With respect to the color difference signals, the time base compression process and the line sequential process are performed. Thereby, record signals in two channels are formed. After the record signal in each channel is FM modulated, it is divided and recorded on two tracks.
FIG. 1 is a block diagram of a playback circuit for playing back an HDTV video disk which has been proposed. In the figure, reference numeral 1 is an optical type disk, on which spiral tracks are formed on one or both surfaces thereof at particular pitches. A spindle servo circuit 3 is provided so that the disk 1 is rotated in a CLV with a spindle motor 2. Reference numeral 4 is an optical head. The optical head 4 is movable in the radius direction of the disk 1 with a feed motor such as a linear motor (which is not shown in the figure). With respect to the optical head 4, a pickup servo circuit 5 for controlling a head feed servo, a tracking servo, and a focus servo is provided.
The optical head 4 diffracts one laser beam into three laser beams which are disposed in closely adjacent positions in the radius direction of the disk 1. The spot of the center beam is positioned at the boundary of the adjacent two tracks. The spots of side beams on both the sides are positioned at the center of each track. The light intensity of the side beams is larger than that of the center beam. With the two side beams, two tracks are played back. By using the difference of playback outputs between the center beam and one side beam and the difference of playback outputs between the center beam and the other side beam, the tracking control is performed. In the above mentioned manner, the disk 1 is played back in parallel on two tracks at a time.
When the playback outputs of the two side beams are named a first channel and a second channel, a playback RF signal in the first channel is sent to an amplifier 11. In addition, a playback RF signal in the second channel is sent to an amplifier 21. An output signal of the amplifier 11 is sent to an FM demodulator 14 through a high pass filter 12 and an RF equalizer 13. The RF equalizer 13 compensates the FM modulation signal for a gain drop in the vicinity of the center carrier frequency. For example, the RF equalizer 13 has a frequency characteristic of a cosine curve. As a demodulation output of the FM demodulator 14, a time-divided an multiplexed signal in the first channel is obtained.
A demodulation output of the FM demodulator 14 is converted into a digital signal by an A/D converter 15. An output signal of the A/D converter 15 is sent to a TBC (time base compensator) 16. The TBC 16 is composed of a memory with a storage capacity in accordance with the compensation amount of the time base fluctuation component and a memory control circuit. By using a write clock WCK with the same time base fluctuation component as the playback signal, the time-divided and multiplexed signal is written to the memory of the TBC 16. By using a reference read clock RCK, the playback component signal is read from the memory. The time-divided and multiplexed signal whose time base fluctuation component was removed by the TBC 16 is sent to a video signal process circuit 29 and an audio signal process circuit 30.
Like the above mentioned playback RF signal in the first channel, the playback RF signal in the second channel is sent to an FM demodulator 24 through an amplifier 21, a high pass filter 22, and an RF equalizer 23. A time-divided and multiplexed signal in the second channel is sent from the FM demodulator 24 to the video signal process circuit 29 and the audio signal process circuit 30 through an A/D converter 25 and a TBC 26.
A demodulation output of one FM demodulator, namely the FM demodulator 24 in this example, is sent to a synchronous separation circuit 27 where a playback horizontal synchronous signal is separated. The playback horizontal synchronous signal is sent to a PLL 28. The PLL 28 generates a write clock WCK which has a frequency that is a multiple of the horizontal frequency and which has the same phase fluctuation component as the playback horizontal synchronous signal. The write clock WCK is sent to the TBC 16 and TBC 26.
An HDTV component signal is composed of a luminance signal Y with a band width of 20 MHz and color difference signals CR and CB with a band width of 6 MHz, each signal having a horizontal synchronous signal. When the component signal is recorded on the disk 1, the time base of the luminance signal Y during one horizontal interval is expanded by 5/3 times. On the other hand, the time base of the color difference signals CR and CB are compressed by 1/2 times. The color difference signals are converted into a line sequential color difference signal where CR and CB are alternatively disposed at each horizontal interval. The time twice the original horizontal interval is referred to as the horizontal interval of a record signal. The luminance signal Y whose time base has been expanded during the new horizontal interval and the line sequence color difference signal CR or CB whose time base has been compressed are time division multiplexed. As an example, at a track in the first channel, a signal where odd numbered luminance signals Y1, Y3, Y5, . . . , and so forth and the color difference signals CB1, CR2, CB5, . . . , and so forth are time division multiplexed and recorded. At a track in the second channel, a signal where even numbered luminance signals Y2, Y4, Y6, . . . , and so forth and the color difference signals CB3, CR4, CB7, . . . , and so forth are time-dividedly and multiplexedly disposed and recorded.
The above mentioned HDTV component signal record method has been proposed by the applicants of the present application and is disclosed in Japanese Patent Application No. SHO 63-335442.
The video signal process circuit 29 serves to separate the luminance signal and the color difference signals, compress the time base of the luminance signal, expand the time base of the color difference signals, and interpolate the color difference signals. The time-divided and multiplexed signals in the channels 1 and 2 are converted into digital component signals (Y, CR, and CB) by the video signal process circuit 29. The component signal is converted into an analog component signal by the D/A converter 31. Thereafter, a playback component signal is obtained from an output terminal 32.
The time base of a PCM audio signal has been compressed during a vertical blanking interval. The audio signal process circuit 30 separates the PCM audio signal, expands the time base, and corrects an error thereof. Thereafter, the audio signal process circuit 30 outputs digital audio signals in two channels. The playback digital audio signals are converted into analog signals by the D/A converter 33 and then obtained from the output terminal 34.
Since the above mentioned HDTV video disk playback apparatus conventionally does not have compatibility with other types of video disks, it is used as a dedicated apparatus for HDTV disks. Thus, when a standard video disk is played back, it is necessary to connect a high definition video disk playback apparatus and a standard video disk play back apparatus to a video monitor which can be used for playing back both the high definition disks and the standard video disks.